grep - print lines matching a pattern
[SYNOPSIS] grep OPTION PATTERN FILE
option
-i Ignore case distinctions in both the PATTERN and the input files
-n Prefix each line of output with the 1-based line number within its input file
-v Invert the sense of matching, to select non-matching lines
-w Select only those lines containing matches that form whole words
-r(R) dir Read all files under each directory, recursively; this is equivalent to the -d recurse option
# grep -r 'word' dir